Noncohering



Patented June 22, 19 37 nonconan'mc, TRANSPARENT srms'rmc orman F.Beach, Rochester, N. Y., assignor, by mesne assignments, to EastmanKodak Com- P y, Jersey City, N. J., a corporation of- New Jersey.

No Drawing. vApplication July26, 1934, Serial N 737,101

, 2, (c1; ifs-51) This invention deals with thin, transparent, celluloseorganic ester sheeting, such as is used in wrapping, packaging, etc.When such sheeting is cut. into sheets, and a large number of the 5sheets are stacked together, ready for use in wrapping or in automaticpackaging machinery, they cohere together, making it difilcult to removea sheet quickly from the pile without wrinkling. This is due to theabsence of air between the perfectly smooth surfaces of the sheets. Thedifllculty is augmented by the strong tendency of cellulose orgamcesters, such as cellulose acetate, cellulose acetate-proplonate, etc.,to accumulate charges of static electricity. The tendency to accumulatestatic and to cohere is many times stronger in cellulose ester sheetsthan in sheets of regenerated cellulose, so that any teaching in the artof regenerated cellulose is of no help with cellulose derivativesheeting.

One object of my invention is to provide thin,

transparent cellulose organic ester sheeting of the wrapping type whichwill not cohere when stacked. Another object is to provide thin,transparent sheeting which willrun smoothly through automatic packagingmachinery. Other objects will hereinafter appear.

I have discovered that thin, transparent sheeting which will fulfill theobjects of my invention may be prepared from cellulose organic csters,by giving to the sheeting an integral surface of cellulose derivative,which surface has been microscopically roughened by the incorporationthereinof a small amount of avery finely divided substance, insufllcientto impair the transparency 85 of the sheeting. By a microscopicallyroughened surface, I mean a surface in which the imperfections arescarcely visible to the naked eye, but are plainly visible with alow-power microscope.

40, In the preferred form of my invention, I incorporate, in thecellulose ester solution or dope used for making the sheeting, a verysmall amount of a very finely divided inorganic pigment, insufllcient toimpair the transparency of the sheet- .45 ing. The pigment which Iprefer to use is extra fine precipitated chalk. I have found that theincorporation of an amount of this pigment equal to 0.25% of the weightof the cellulose ester is sufficient to keep the finished sheeting fromco- 5 hering, and from jamming in automatic packaging machinery.

In preparing the solution or dope for making the sheeting, I may, by wayof example, proceed as follows: 100 parts of cellulose acetate is dis-55 solved, with agitation, in-from 400 to 600 parts,

by weight, of acetone or othercellulose acetate solventor solventmixture. From 10 to 50 parts of a suitable cellulose acetateplasticizer, such, for instance, as monochloronaphthalene or diethylphthalate, is incorporated in the solution, and approximately 0.25%,based on the weight of the cellulose acetate, of extra line precipitatedchalk is added to the solution and uniformly distributed therethrough bythorough mixing. The dope is then spread in a very thin layer on ahighly polished surface, in .a manner well known for the preparation of'sheeting, the solvent is evaporated from the layer, and the layerstripped with the cellulose ester may be used. In place of precipitatedchalk, I may use other inorganic pigments, such, for instance, as thevarious forms of alumina, talc, silica, titanium dioxide, bariumsulfate, or tripoll. It will be observed that I use the term pigment notin the strict sense in which it is used in the paint industry, but morenearly as it is used in the rubber industry, to mean any finely divided,insoluble inorganic substance, regardless of its tinctorial or hidingpower. If

from the polished surface; The finished sheetthe sheeting is to be usedfor wrapping food products, it will be evident that both the plasticizerand the pigment used should be non-toxic. I The weight of pigment to beused will vary somewhat with the specific gravity and particle size ofthe pigment, but maybe readily determined by trial. In place ofinorganic pigments, I may use organic powders, such as lycopodium,various carbohydrates (e. g. dextrin, starches and sugars) gelatins, orfinely divided cellulose esters which are insoluble or incompletelysoluble in the solvent or solvent mixture'used in making the dope. Or, Imay add to the clear dope a small amount of a grainy cellulose organicester dope, i. e., a cellulose organic ester solution containing acellulose organic ester which is imperfectly soluble in the solventused.

In any case, the amount of pigment or other insoluble substance usedmust be so small that the of theiinished, meet. u not impaired. I amaware that rested surfaces have been produced on sheeting by variousmeans,

suchas by-coating on a roughened 'plate.. Also.

This has obvious disadvantages in that the talc soils the sheets; ;rubson; etc. My-inventionis unique in providing a-t'ransparent ceih rlose organic ester sheeting having an integral. cellulose organic ester surfacemicroscopicaliy rouahened by the incorporation of a small solublematerial.

I'prei'er to avoid the useioi any ""subbinl' o eration, i. e.,coating-0t formed sheetingwith at liquid by means of an applicatorroil,ismaylns. I

etc. However, it is possible to coat ordinary cellulose organic estersheeting with a ,layerofcellm A lose derivative dope containingfinelytdivided ink soluble substances (such as that described above) inamountinsuflicient to impair the transparency of the sheet, and I regardthis as coming withinv the broad scope of my inventlominasmuch as ity-bu --the:sheet." I v v H v 25A estersheet orthe 1 finely divided'chalkinan amount qiial'to fromv roughened.

What-I claimfasm wr s e m ture besccured byLctter'sPatent onneqnite smesithasbeenproposed,topromoteslippalebetweenis .6 thin sheets by coatingwith a layer oi talc;

"1: -tr nsparent. cell lbscacetatesheet approximatclyrbl the w'cigh tictecumenicatate;.. the amount otchaik being suflicient, m comcalyrovshsntho nutmofthesheet v.

. nt 9 im he Where! the cellulose moi-g m amount of,

sumcient to Musli the of the-sheet, but'insufllcient to 'impaifthetransparencyot the sheet. a a

